FR2669865A1 - TRANSMISSION ASSEMBLY FOR ALL-TERRAIN VEHICLES WITH FOUR DRIVE WHEELS, ESPECIALLY TRACTORS. - Google Patents

Abstract

The invention relates to a transmission assembly by which the front wheels of a tractor can be driven by means of a set of two overrunning couplings (11, 12) which can transmit torque in opposite directions of rotation. and which respectively switch to the free position for the other direction of rotation, the freewheel couplings (11, 12) being able to be coupled or decoupled with the driving device (13), by means of clutches (42, 43). The actuation is effected by means of a control unit (56) which, depending on the position, urges or releases the friction assemblies of the clutches (42, 43), and which, however, takes a priority position in which the two clutches (42, 43) are in the torque transmission position, with a view to braking the front wheels by means of the rear wheels.

Description

TRANSMISSION ASSEMBLY FOR ALL VEHICLES

  FOUR-WHEEL DRIVE FIELDS, PARTICULARLY

TRACTORS.

  The invention relates to a transmission assembly for an all-terrain four-wheel drive vehicle, in particular a tractor, which has a permanent drive for the rear wheels, and the front wheels of which can be made drive via a line. transmission derived from rear wheel transmission, a freewheel coupling capable of being brought into a torque transmission position in the desired direction of propulsion, being provided for each of the directions of rotation resulting from the two directions of drive drive forward and reverse, each of these freewheel couplings being able to be coupled to the driving device by means of a clutch, the freewheel couplings being arranged side by side in an axial direction, and the two clutches being associated with an element leading common and capable of being brought, by a common actuating member, into control positions in which respectively one of

  clutches is made active and the other inactive.

  Such a transmission assembly is disclosed for example by document DE-OS 25 12 431 This assembly and this configuration however lead to the fact that the torque can, in each case, only be

transmitted in one direction.

  Document DE 34 07 918 A 1 shows an assembly in which a freewheel coupling is

  integrated in the transmission line to the front wheels.

  In the case of this solution, torque transmission is also possible only in one direction. However, there are also driving situations for which a rigid coupling is desired. This cannot however be achieved with known solutions. The object of the invention is to create a transmission assembly for which, apart from the torque transmission which can be selected as desired, by means of one of the freewheel couplings, it is also possible to produce a rigid coupling for torque transmission of the two axles. According to the invention, this object is achieved thanks to the fact that the actuating member can be brought into a position in which the two clutches are connected to the driving device, and that

  this position is the priority position.

  The advantage of such a configuration lies in the fact that thanks to the locking position as a priority position, the front wheels are, in particular when stationary, braked by the stopping brake acting only on the rear wheels Par Furthermore, the drive link of the two axles also engages automatically in the event of an actuation failure. It is also advantageous in the case of this embodiment, to be able to materialize, both for reverse and for forward, a drive mode which avoids deformation and which allows, in particular for example to the front wheels, as long as '' they still move without slipping on firm ground, to turn at a higher angular speed than the rear wheels The front wheels are therefore ahead This is particularly favorable in the case of traffic in curves, because the reduction can be chosen so that the faster rotation being established for a front wheel in the case of traffic in curves, cannot lead to deformations It is only when the advance is compensated by the sliding on the rear wheels, that the front wheels are made drive These conditions are valid for both forward and reverse, because two couplings are provided at ro free, one of which is respectively made active for one of the directions of propulsion For this purpose, the operation making it active or inactive can be carried out by an automatic control member, which can for example be influenced by the respective gear change for forward and reverse The operation to make active or inactive or switching respectively to the other direction of propulsion, can be carried out when the brake is actuated, to thus include the front wheels during the braking phase A connection to the wheels of the front axle is then established for the braking torque Indeed, on tractors, most often

  only the rear wheels are fitted with brakes.

  A particularly compact construction is obtained by the fact that the freewheel couplings comprise a common freewheel hub and, however arranged coaxially therewith, freewheel bushings, however separate, and by the fact that between the hub freewheel and each of the freewheel bushings are arranged locking bodies capable of being brought in, according to directions

  opposite, in the torque transmission position.

  The clutches can be of different configuration depending on the use case In the case where one wishes a flexible passage in integral traction, and that overloads must be possible without rupture of parts, it is proposed according to another configuration of the invention, that the clutches are in the form of friction clutches, that first clutch lamellae are associated by rotationally but axially sliding connection with the freewheel sockets of the freewheel couplings, and are arranged in alternating with second clutch plates associated with the driving element, that the clutch plates of the two clutches are urged by a pressure ring which is connected by a rotation link, but axially sliding, to the element leading, and that the two pressure rings are biased by common springs bearing

between them.

  For actuation, provision is made for the actuating member in the form of a control bell which can slide axially and having control surfaces capable of being brought to bear against the pressure rings, to make

inactive the clutches.

  As a variant, it is provided that the clutches are in the form of clutch clutches, that the freewheel sockets of the freewheel couplings each comprise a first clutch ring which is linked to them in rotation and which comprises clutches , as well as a second clutch ring movable axially with respect to the first clutch ring and comprising dogs which can be brought into engagement with the first, these second clutch rings being connected by a rotation link, but axially sliding to the driving element, and the two second clutch rings are biased, by common springs bearing between them, in the direction of the first two

clutch rings.

  For the actuation of clutches in the form of dog clutches, the actuation member is produced in the form of a control bell which can be moved axially and having control surfaces capable of being brought into support against the axially displaceable clutch rings, to make the

clutches.

  Furthermore, it is possible to carry out an embodiment comprising clutches in the form of clutches with locking bodies. Concretely in this case, the freewheel sockets of the freewheel couplings are rotatably housed in a driving element having the of a driving sleeve For locking, the driving elements comprise, for each freewheel sleeve, one or more locking elements guided radially in passage openings and capable of being brought into or out of engagement by complementarity of form with snap-in recesses in the freewheel sockets, these locking elements being held respectively in the locking position by a locking ring spring-loaded and capable of sliding axially They can be moved out of it by the member d actuation, against the force of the springs which urge them, in a p release position

  for locking elements.

  For actuation, provision is made for the actuator to be produced in the form of a control bell which can slide axially and having control surfaces capable of being brought to bear against the displaceable locking rings.

  axially, to make the clutches inactive.

  According to another configuration, it is proposed to actuate these clutches by an actuating member

  common which can be controlled by a control unit.

  The embodiment of the control unit and of the actuating member allows the control unit to assume the locking position when the actuating forces fail or when the vehicle stops. a drive link between the two axles, when the engine stops or in the event of

  control system failure.

  According to another configuration of the invention, there is provided for the displacement of the control bell, namely of the actuating member, a control unit constituted by a piston and cylinder unit capable of being stressed by a fluid under pressure One of the constituent parts of this unit, preferably the cylinder, is mounted in a fixed position, while the other of the constituent parts which is sliding, preferably the piston, carries the control bell via of a bearing allowing the rotational movements Thus, the control bell can rotate freely with the clutches associated with the freewheel couplings The transmission of the displacement forces takes place via the bearing which is preferably provided

in the form of a bearing.

  According to a configuration of the invention, it must also be possible to completely separate the driving device, both for forward movement and for reverse gear. To achieve this, there is provided for the actuating member, an intermediate position constituting another control position for which the two freewheel couplings are separated from the driving device by means of the clutches. The invention will now be described with reference to embodiments and uses which are shown schematically in the accompanying drawings which show: FIG. 1 a four-wheel drive tractor comprising the transmission assembly according to the invention , Fig 2 a longitudinal section of the unit composed of clutches and freewheel couplings, along the line BB of Figure 3, Fig 3 a cross section along the line AA of Figure 2, Fig 4 a variant with respect to the configuration according to Figure 2, Fig 5 a longitudinal section of a unit comprising as clutches, friction clutches, Fig 6 an embodiment of the unit comprising as clutches, dog clutches. In FIG. 1 is shown a tractor 1 which is driven by a motor 2 The motor 2 drives a gearbox 3 by which the rear wheels 5 are driven, by means of transmission shafts 4 From the gearbox speeds 3 or a rear axle differential, is carried out, by means of a transmission unit 6 explained in more detail with reference to FIGS. 2 to 5, the drive of the longitudinal shaft 8 which drives the front wheel differential 9 From this is derived the drive movement for the two front wheels 7, by means of transmission shafts 10. In FIGS. 2 and 3, the transmission unit 6 which is clamped on the gearbox

  3, is shown in detail and on an enlarged scale.

  The transmission unit 6 comprises two freewheel couplings 11, 12 one of which, namely the freewheel coupling 11 is intended for the transmission of the torque in the forward direction of the tractor 1, while the freewheel coupling 12 can transmit a torque in the other direction of rotation, for reverse gear The driving element 13 is produced in the form of a bushing, one end of which is provided with a flange 14 on which is fixed a driving gear receiving its rotational movement from the gearbox 3 With the driving gear 15, is at the same time fixed by screwing using the fixing screws 16 assigned to the gear, a sleeve bearing 17 which for mounting the unit, carries a bearing 18 which

  is mounted in the transmission unit housing 6.

  The bearing sleeve 17 is hollow and is used for the passage of a pin or the like to be driven. The other end of the driving element 13 in the form of a sleeve is also connected to a bearing pin 19, which is mounted to rotate in the casing of the transmission unit 6, by means of another bearing 20 In the bore 21 of the driving element 13 in the form of a bushing, the two free wheel bushings 22, 23 of the two couplings are rotatably mounted freewheel 11, 12 For this purpose, the two freewheel bushings 22, 23 are axially separated from each other by means of an intermediate ring 30 By means of wear washers 24 and stop rings 25, the locking pawls 26, 27 and the freewheel hub 28 common to the two freewheel sockets 22, 23, are rotatably housed in the mounting bore 29 The freewheel sockets 22, 23 include, as can be seen in FIG. 3 with regard to the freewheel coupling 11, locking pawls 26 as a locking body, which are capable of being brought into abutment against a bearing surface 32 of a recess in the freewheel sleeve 22 The pawls of locking 26 are also biased radially outward towards the bearing surface 32, in a recess 33 of the freewheel hub 28, by a spring 34 When the freewheel sleeve 22 of the freewheel coupling It is driven in a rotation to the left (direction of rotation N), a torque is transmitted from the freewheel bush 22, via the bearing surface 32, on the locking pawl 26 and from this. on the freewheel hub 28, by means of bearing surfaces 31 The freewheel hub 28 has a grooved bore 35 which is used for driving, for example, the longitudinal shaft connected by means of a trunnion at freewheel hub 28, and therefore between ment of the front wheels 7 of the tractor 1 in accordance with FIG. 1, and this in the direction of a forward drive The freewheel coupling 23 is of configuration substantially symmetrical with respect to an axis of symmetry formed by the intermediate ring Here, the locking pawls 27 are arranged so that they are active in a direction opposite to the direction of drive rotation N shown in FIG. 3 and relating to the freewheel coupling 11, so that that for a drive in a direction of rotation to the right of the driving element 13, a torque is transmitted to

the freewheel bush 23.

  The driving element 13 being in the form of a socket has two spaced rows, of several passage openings 36, 37 extending radially and distributed over the periphery, in which are movably guided in the radial direction, elements Locking device in the form of locking balls 38, 39 According to the sectional representation of FIG. 3, four locking balls 38 distributed over the periphery are provided in total as regards the freewheel coupling 11 latching 40, 41 are provided with a corresponding peripheral distribution in the freewheel bushings 22, 23; in these recesses are engaged the locking balls 38 for the switching position shown with regard to the freewheel coupling 11 The locking balls 38, 39, the passage openings 36, 37 in the driving element 13 and the snap-in recesses 40, 41 in the two freewheel sockets 22, 23 are component parts of clutches 42, 43, the clutch 42 of which is associated with the freewheel coupling 11, and the clutch 43 the freewheel coupling 12 A locking ring 44 is associated with the clutch 42 to lock the locking balls 38 in their torque transmission position, and is guided axially sliding on the outer surface 46 of the leading element 13; in its position moved to the right shown in Figure 2, this locking ring keeps captive, with its inner surface 47, the locking balls 38 in their position of radial displacement towards

  inside, in the snap-in recesses 40.

  Thus, a torque transmission link is produced between the driving element 13 and the freewheel sleeve 22, via the passage openings 36 of the driving element, locking balls 38 and snap-in recesses 40 The locking ring 44 is biased towards this position by springs 48 which bear on the one hand on it and on the other hand on the flange 14 In this locking position where it is moved to the right, the lock ring 44 bears against a stop ring 50. The freewheel coupling 12 is not active in the position shown in FIG. 2 A torque transmission link is not established between the driving element 13 in the form of a sleeve and the freewheel sleeve 23, because the locking balls 39 are in their outermost radial position, in the passage openings 37 and are not engaged with the latching recesses 41 of the doui The freewheel 23 In this position, the locking balls 39 penetrate into a contour 51 of the locking ring 45 To be able to be brought into this position, there is a control bell 52 which has a collar 53 bent radially towards

  the interior and forming two control surfaces 54, 55.

  In the case of the position shown in Figure 2, the control surface 54 is applied against the locking ring 45 and moved the latter to the right against the force of the springs 49, by means of a movement movement of the control bell 52 by means of a control unit 56, so that the locking balls 39 can be moved freely towards the outside. The control bell 52 is mounted by means of a bearing 57 on a bearing ring 59 mounted axially sliding on a base 58 of the casing, this assembly allowing the relative rotation of the control bell relative to the bearing ring The bearing ring 59 is connected to a piston 62 of the control unit 56, via a connecting yoke 61 connected to the ring by means of pins 60 The piston 62 can slide axially in the cylinder 63 If the control unit 56 is actuated in such a way that the piston 62 is d carried to the left from the position shown in Figure 2, the control bell 52 is at the same time moved to the left by means of the connecting yoke 61, pins 60, the bearing ring 59 and the bearing 57 The locking ring 45 is released and can move to the left under the effect of the force of the springs 49, the locking balls 39 being able to move on this occasion radially inwards, in the snap-in recesses 41, in order to produce a rotational connection between the driving element 13 and the freewheel sleeve 23 The control surface 54 of the control bell 52 moves away on this occasion from the locking ring 45, towards the stop ring 50 The locking ring 45 is moved to the left until it comes to bear against the stop ring 50, under the effect of the force of the spring 49 The axial dimensioning, i.e. the axial distance separating the from ux control surfaces 54, 55 corresponds substantially to the thickness of the stop ring 50 When the collar 53 is radially outside the stop ring 50, but in an axial position in alignment with that of the ring stop 50, the two clutches 42, 43 are in their engaged position In this case, is established in both directions of rotation, a rigid coupling between the driving element 13 and the free wheel sockets 22, 23 of the two wheel couplings free 11, 12, and therefore a rigid connection with the freewheel hub 28, by means of the locking pawls 26, 27 If the movement to the left of the control bell 52 is continued by means of the control unit 56, the control surface 55 bears against the locking ring 44 of the clutch 42 and moves it to the left against the force of the spring 48, so that the interior surface 47 is axially distant from the glass beads tool 38 and frees them by allowing them to radially escape from

snap-in recesses 40.

  In the switching position shown in FIG. 3, a torque transmission can take place in the direction of rotation N, while in the switching position described above, for which the control bell 52 moves the locking ring 44 to the left, a torque transmission can take place against the direction of rotation N In the direction of rotation respectively different from the direction of transmission, an advance can occur It is thus for example possible, in the case of the switching position shown in FIGS. 2 and 3, that the freewheel hub 28 when it rotates in the direction of rotation N, is in advance on the sleeve

  freewheel 22, i.e. rotates faster than this

  this. In the case of the embodiment shown in FIG. 4, this is a variant with respect to the embodiment of FIGS. 2 and 3 The two locking rings 44, 45 are arranged so as to be separated from each other on the other, by means of springs 48 distributed over the periphery and resting axially on them The control bell 52 has two stops 54, 55 which act on the locking rings 44, 45 In FIG. 4, the control bell 52 is in the position where it is moved to the right Correspondingly, the locking ring 44 is moved to the right in its open position, by the action of the stopper 55 The ring of lock 45 is on this occasion pushed into its locking position, by the springs 48 The locking balls 39 engage in the recesses of

  locking 41 of the freewheel sleeve 23.

  Freewheel coupling 12 is linked to the element

  leading 13 and therefore training.

  Regarding the embodiment shown in Figure 5, the freewheel couplings 11, 12 correspond to those described with regard to Figures 2 and 3 The only difference lies in the configuration of the clutches 42, 43, which in this example embodiments are produced in the form of friction clutches The two clutches 42, 43 being in the form of friction clutches, each comprise first clutch plates 64, which are connected axially sliding but fixed in rotation , to the driving element 13 which is provided for this purpose with suitable grooves Furthermore, second clutch plates 65 are provided provided with projections which engage axially sliding but fixed in rotation, in grooves 66 provided on the outer periphery of the freewheel sockets 22, 23 The first clutch plates 64 are mounted alternately with the second clutch plates 65 L clutch plates 64, 65 of the clutch 42 in the form of a friction clutch, bear axially against an inner front wall 67 of the driving element 13, while the clutch plates 64, 65 of the second clutch 43 bear axially against a support ring 69 held by a stop ring 68 on the driving element 13 The friction assemblies constituted by the clutch plates 64, 65 of the two clutches 42, 43 , are each biased by a pressure ring 70, 71, these pressure rings being reciprocally separated by springs 72 disposed between them, and biasing the friction assembly of the two clutches 42, 43 In the position shown in FIG. 5, the two clutches 42, 43 are urged so that there is a locking of the two freewheel couplings 11, 12 If the control bell 52 is moved to the left from the position shown, it comes put on n supported by its control surface 54, against the pressure ring 71 of the clutch 43, and discharges the friction assembly composed of the clutch plates 64, 65 of the clutch 43, continuing its movement, c '' is to say by stressing the control unit 56 and therefore the piston 62 for the movement to the left, so that it is only still possible to transmit a torque by the freewheel coupling 11 If on the contrary, the control unit 56 is biased in pressure so that the piston 62 moves to the right, the control surface 55 of the control bell 52 comes to bear against the pressure ring 70 of the clutch 42 and discharges its friction assembly, while simultaneously, by moving the control surface 54 away from the pressure ring 71, the friction assembly of the clutch 43 is again acted upon In this position, a torque transmission can be done through the coupling ent with freewheel 12, while the coupling with freewheel 11 is completely disconnected from the torque transmission in the two directions of rotation. In the case of the embodiment shown in FIG. 6, the two clutches 42, 43 are produced in the form of dog clutch The two freewheel couplings 11, 12 essentially correspond to the configuration of those described in look at the previous figures In the case of the embodiment according to FIG. 6, first clutch rings 73, 74 are associated with the two bushings

  freewheel 22, 23 and are linked in rotation thereto.

  They have in a front surface, dogs 77, 78 which cooperate with combined dogs of second clutch rings 75, 76 being able to transmit a torque when they are engaged. The second clutch rings 75, 76 are housed in fixed in rotation but axially sliding, in slots of the driving element 13 Between the two second clutch rings 75, 76 are axially supported springs 72 which urge the two second clutch rings 75, 76 to come in taken with the dogs 77, 78 of the first clutch rings 73, 74 In the position shown, the two clutches 42, 43 are engaged, so that there is a rigid connection for the two directions of rotation by coupling the two Freewheel couplings 11, 12 Here also, as an actuating element, there is provided a control bell 52 axially sliding under the effect of a control unit 56 in the form of a piston unit and cylind re, this control bell 52 having control surfaces 54, 55 by means of which the second clutch rings 75, 76 can be moved Thus, by displacement of the control bell 52 to the left, by means of the control unit 56, the control surface 54 can be brought to bear against the second clutch ring 76 of the clutch 43, and by continuing the stress, displaces the latter against the force of the springs 72, to the left in the direction of the second clutch ring 75 of the first clutch 42 which is assigned to the freewheel coupling 11 On this occasion the dogs 78 and the combined dogs are brought out of engagement The transmission link of torque between the driving element 13 and

  the freewheel coupling 12 is thus interrupted.

  Only the freewheel coupling 11 is still active.

  During the movement of the control bell 52 to the right, the control surface 55 comes to bear against the second clutch ring 75 and moves the latter so as to bring out of engagement its clutch dogs combined with dogs 77 of the first ring clutch 73, so that the clutch 42 is out of engagement, while the second clutch ring 76 is biased in the direction of the first clutch ring 74 of the clutch 43, its dogs 78 engaging taken with the combined dogs, so that a torque transmission connection is established between the driving element 13 and the freewheel socket 23 of the freewheel coupling 12 In this switching state, a torque can be transmitted only through

freewheel coupling 12.

Claims (9)

CLAIMS.   1 Transmission assembly for an all-terrain four-wheel drive vehicle, in particular a tractor, which has a permanent drive for the rear wheels, and the front wheels of which can be made drive via a transmission line derived from the transmission of the rear wheels, a freewheel coupling capable of being brought into a torque transmission position in the desired direction of propulsion, being provided for each of the directions of rotation resulting from the two driving directions forward and reverse , each of these freewheel couplings being able to be coupled to the driving device by means of a clutch, the freewheeling couplings being arranged side by side in the axial direction, and the two clutches being associated with a common driving element and susceptible to be brought, by a common actuator, into control positions in which the one of the clutches is made active and the other inactive, characterized in that the actuating member can be brought into a position in which the two clutches (42, 43) are connected to the driving device (13), and in that that this position is the position priority.   2 transmission assembly according to claim 1, characterized in that the freewheel couplings (11, 12) comprise a common freewheel hub (28) and arranged coaxially therewith, freewheel bushings (22, 23 ) however separate, and in that between the freewheel hub (28) and each of the freewheel bushings (22, 23) are arranged locking pawls (26, 27) capable of being brought in, according to directions opposite, in position of torque transmission.   3 Transmission assembly according to one of   claims 1 or 2, characterized in that the   clutches (42, 43) are in the form of friction clutches, in that first clutch plates (64) are associated by rotationally but axially sliding connection with the freewheel sockets (22, 23 ) freewheel couplings (11, 12), and are arranged alternately with second clutch plates (65) associated with the driving element (13), in that the clutch plates (64, 65) of the two clutches (42, 43) are urged by a pressure ring (70, 71) which is connected by a rotation link, but axially sliding, to the driving element, and in that the two pressure rings (70, 71) are requested by   common springs (72) resting on each other (Figure 5).   4 Transmission assembly according to one of   claims 1 or 2, characterized in that the   clutches (42, 43) are in the form of dog clutches, in that the freewheel sockets (22, 23) of the freewheel couplings (11, 12) each comprise a first clutch ring (73 , 74) which is linked to them in rotation and which comprises dogs (77, 78), as well as a second clutch ring (75, 76) movable axially with respect to the first clutch ring and comprising dogs (77 , 78) capable of being brought into engagement with the first, these second clutch rings being connected by a rotation link, but axially sliding to the driving element (13), and in that the two second rings clutch (75, 76) are biased by common springs (72) resting against each other, towards the first two rings clutch (73, 74) (Figure 6).   Transmission assembly according to one of   claims 1 or 2, characterized in that the   clutches (42, 43) are in the form of lock body clutches, in that the freewheel sockets (22, 23) of the freewheel couplings (11, 12) are rotatably housed in an element driving (13) in the form of a driving sleeve, in that this driving element comprises for each freewheel sleeve (22, 23), one or more locking elements (38, 39) guided radially in openings passage (36, 37) and capable of being brought into or out of engagement by complementarity of form with snap-in recesses (40, 41) in the freewheel sockets (22, 23), these locking elements (38, 39) being held respectively in the locking position by a locking ring (44, 45) biased by a spring and capable of sliding axially, and these locking rings being able to be moved out of this position by the actuating member (52), at the meeting re of the force of the springs (48, 49) which urge them, to bring them into a release position for the   locking elements (38, 39) (Figure 4).   6 transmission assembly according to claim 3, characterized in that the actuating member is made in the form of a control bell (52) which can slide axially and having control surfaces (54, 55) capable of be brought into abutment against the pressure rings (70,   71), to make the clutches inactive (42, 43).   7 transmission assembly according to claim 4, characterized in that the actuating member is made in the form of a control bell (52) which can be moved axially and having control surfaces (54, 55) capable of '' brought into abutment against the axially movable clutch rings (75, 76), to make the clutches (42, 43) are inactive.   8 transmission assembly according to claim 5, characterized in that the actuating member is produced in the form of a control bell (52) which can slide axially and having control surfaces (54, 55) capable of be brought into abutment against the axially movable locking rings (44,), to make the clutches (42, 43).   9 Transmission assembly according to one of   claims 1 to 8, characterized in that the member   actuator (52) common to the two clutches (42, 43)   can be controlled by a control unit (56).   Transmission assembly according to claim 9, characterized in that the control unit (56) is a piston and cylinder unit capable of being stressed by a pressurized fluid, and one of the constituent parts of which is mounted in position fixed, while on the other of the constituent parts which is sliding, the control bell is mounted by means of a bearing (57)   allowing rotational movements.   11 transmission assembly according to claim 1, characterized in that the actuating member (52) can in addition be brought into another control position for which the two freewheel couplings (11, 12) are separated from the device leading (13) through clutches (42, 43).